Method for estimating the movement of an object moving in a magnetic field

Abstract

A method for estimating the movement of an object moving in an ambient magnetic field. The method acquires at least one component of the magnetic field and/or an i-th derivative of the magnetic field measures at least one item of information representative of the movement of the object; evaluates the stationary or otherwise character of the magnetic field; estimates at least one component of the movement of the object using at least one equation other than magnetic linking the component of the movement of the object and the at least one acquired item of information representative of the movement of the object depending on the result of the evaluation at least one magnetic equation linking the component of the movement of the object and the at least one acquired component of the magnetic field and/or an i-th derivative of the magnetic field.

The invention claimed is: 
     
       1. A method for estimating movement of an object moving in an ambient magnetic field, the method comprising the steps of:
 (a) Acquisition:
 by a magnetic measurement unit fixed with respect to said object, of at least one component of the magnetic field and/or an i-th derivative of the magnetic field, at the magnetic measurement unit; 
 by a measurement unit other than magnetic fixed with respect to said object, of at least one item of information representative of the movement of the object; 
 
 (b) Calculation, by a data processor, of a parameter representative of a stationary or otherwise character of the magnetic field at the magnetic measurement unit; 
 (c) Estimation, by the data processor, of at least one component of the movement of said object using,
 at least one equation other than magnetic linking said component of the movement of said object and the at least one acquired item of information representative of the movement of the object; 
 according to the calculated value of the parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit, at least one magnetic equation linking said component of the movement of said object and the at least one acquired component of the magnetic field and/or an i-th derivative of the magnetic field. 
 
 
     
     
       2. The method according to  claim 1 , in which the magnetic measurement unit includes a plurality of gradiometers and/or magnetometers organised into triaxes, each triaxis being associated with a spatial position. 
     
     
       3. A non-transitory storage medium readable by a computer equipment, having stored thereon instructions for the execution of a method for estimating the movement of an object moving in an ambient magnetic field according to  claim 1 . 
     
     
       4. The method according to  claim 1 , in which the magnetic equation(s) are of the form ∇ n   ⋅ B=f n (Ω)·∇ n B+g n (∇ n+1 B)·V, where ∇ n B is an n-th derivative of the magnetic field, Ω the instantaneous angular velocity, V the instantaneous linear velocity, and f n  and g n  predetermined functions. 
     
     
       5. The method according to  claim 4 , in which the magnetic equation is {dot over (B)}=−Ω×B+∇B·V. 
     
     
       6. The method according to  claim 1 , in which:
 said measurement unit other than magnetic is a inertial measurement unit, such that said acquired information representative of the movement of the object is at least one component of an acceleration and/or an angular velocity of the object; 
 said at least one equation other than magnetic is an inertial equation linking said component of the movement of said object and the at least one acquired component of an acceleration and/or an angular velocity of the object. 
 
     
     
       7. The method according to  claim 6 , in which step (a) includes the acquisition, by the inertial measurement unit, of three components of the acceleration of the object and three components of the angular velocity of the object. 
     
     
       8. The method according to  claim 1 , in which said parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit is a numerical value, the at least one magnetic equation having a variable contribution in step (c) as a function of the calculated value of said parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit. 
     
     
       9. The method according to  claim 8 , in which step (b) includes the calculation of an innovation of a state observer, said parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit being a function of said innovation. 
     
     
       10. The method according to  claim 9 , in which said parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit is the difference between the theoretical trace of the covariance matrix of the innovation, and the estimated trace of the covariance matrix of the innovation. 
     
     
       11. The method according to  claim 8 , in which step (c) includes the implementation of a state observer to estimate a state including said at least one component of the movement of said object, the contribution of said at least one magnetic equation being controlled via a gain of said state observer. 
     
     
       12. The method according to  claim 11  in which step (b) includes the calculation of an innovation of a state observer, said parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit being a function of said innovation and the state observer implemented at step (c) is a state observer used at step (b). 
     
     
       13. An equipment for estimating movement of an object moving in an ambient magnetic field, including a data processor configured to implement:
 a module for receiving:
 at least one component of the magnetic field and/or an i-th derivative of the magnetic field, acquired by a magnetic measurement unit fixed with respect to said object, 
 at least one information component representative of the movement of the object, acquired by a measurement unit other than magnetic fixed with respect to said object, 
 
 a module for calculating a parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit; 
 a module for estimating at least one component of the movement of said object using,
 at least one equation other than magnetic linking said component of the movement of said object and the at least one acquired item of information representative of the movement of the object; 
 according to the calculated value of the parameter representative of the stationary or otherwise character of the magnetic field at the magnetic measurement unit, at least one magnetic equation linking said component of the movement of said object and the at least one acquired component of the magnetic field and/or an i-th derivative of the magnetic field. 
 
 
     
     
       14. The equipment according to  claim 13 , being a case including the magnetic measurement unit and the measurement unit other than magnetic. 
     
     
       15. The equipment according to  claim 14 , being a mobile terminal or a server, suited for communicating with a case including the magnetic measurement unit and the measurement unit other than magnetic. 
     
     
       16. A system including the equipment according to  claim 15  and at least one connected case.